Objectives: To develop drugs for treatment and prevention of multidrug resistant malaria that are safe for use in children and pregnant women and that may be co-formulated with other drugs for prevention and treatment of active infections, for transmission blocking, and to aid in worldwide efforts to eradicate the disease. Introduction: For each of the estimated ?1 million people killed each year by malaria there are hundreds that are severely sickened by the disease. Indeed, malaria is one of the most frequent causes of sickness and death in the world today but especially in sub-Saharan Africa where its victims are primarily young children and pregnant women. And the situation is worsening due to the spread of Plasmodium strains that harbor resistance to multiple drugs including the quinolines chloroquine (CQ), amodiaquine (AQ), quinine and mefloquine. In some areas of the world, especially in SE Asia, multidrug resistance (MDR) has forced an absolute reliance on the artemisinin combined therapies for treatment of malaria. And now there are reports of increasing response times and artemisinin resistance in malaria parasites from Cambodia. Findings to date: We have used sontochin (SQ) as a guide to create pharmachins with alkyl or aryl substituents at the 3-position of the 4-aminoquinoline core. Modified with an aryl substituent PH-203 exhibits low nM IC50 values against MDR strains and in vivo efficacy against patent infections of P. yoelii in mice that is superior to CQ. With SQ and PH-203 as structural leads for optimization we have generated a library of >300 analogs varying the aryl substituent at the 3-position while optimizing the scaffol for in vitro activity and in vivo efficacy. Our results show that 3-position aryl pharmachins represent potential CQ and AQ replacement drugs. From here to there: We discovered that SQ is active against MDR P. falciparum strains. We then replaced the 3-position CH3 group with an aryl ring to produce analogs with impressive low nM IC50's vs. MDR strains, low ED50's vs. murine malaria, that were curative at 16 mg/kg in the 4-Day Peters test. Our efforts to optimize the 3-position aryl substituent as well as the 4-position side chain continue. For the proposed work we will focus on 3-position alkyl pharmachins, to optimize a sub-series with impressive antimalarial properties. Consider PH- 255with single digit nM IC50 values against MDR falciparum strains and with an ED50 value of less than 0.5 mg/kg against patent malaria infections in mice. Specific Aims: 1. To evaluate and optimize 3-position alkyl-pharmachins for antimalarial activity in vitro against MDR resistant strains of P. falciparum and in vivo vs. a rodent species of malaria, P. yoelii, 2. To evaluate and optimize 3-position alkyl-pharmachins for metabolic stability (t1/2) and fate in both murine and human microsomal systems and assessment of pharmacokinetics in vivo (in mice), 3. To conduct in vitro risk assessment tests on selected 3-position alkyl-pharmachins for potential genotoxicity in a prokaryotic system (Ames tests) and hERG channel inhibition, and 4. To establish the propensity for (and including mechanism of) 3-alkyl-pharmachin resistance in P. falciparum parasites (Dd2) in vitro. Methods: We will follow a standard drug optimization routine involving iterative synthesis and screening of 4- aminoquinoline analogs of the our lead 3-alkyl-pharmachins to enhance: in vitro potency against MDR P. falciparum parasites including clinical isolates from Cambodia with resistance to artemisinin; in vivo efficacy in malaria infected mice, metabolic stability, pharmacokinetics and safety. VA relevance: We seek to develop a safe CQ replacement drug for treating and preventing malaria without the neurological side effects of existing alternatives such as mefloquine. Rapid therapeutic intervention with a cocktail of safe antimalarial agents may avoid unnecessary toxic exposures (i.e., febrile conditions compounding the stress of warfare and combat readiness) that may otherwise have enduring long-term health consequences.